The first settlers in what is today the parish of Carrigallen came there during the Stone Age, sometime between the year 4 and 15 BC. We know this from the scant remains they left behind in the form of megalithic tombs which they built as burial places for their dead. Professors Ruairi De Valera and Seán Ó Nuallain, in their Survey of the Megalithic Tombs of Ireland, published in 1972, mention two megalithic ruins in the parish of Carrigallen, both in such a poor state of preservation as to make it impossible to say with certitude that they were megalithic tombs. The first of these is at Newtowngore, described on the Ordnance Survey map as a 'Druid's Altar'.

The second in Longfield, which is referred to on the Ordnance Survey map as a Giant's Grave is described by De Valera and Ó Nuallain as a densely overgrown moun measuring approximately 11m long (N-S), 7m wide (E-W) and reaching a height of at least a metre. The northern end of the mound runs into a thick field fence. A line of three erectstones running north-south is visible 2metres inside the western edge of the mound. There are also a number of standing stones on a hill overlooking Calloughs Lake but again there is no evidence to authenticate these stones as the remains of a megalithic tomb and De Valera and Ó Nuallain don't even mention them in their survey.

The ring forts, of which there are eighteen in the parish, belong to a later period. They are the ruined homesteads of late Bronze Age farmers. They continued in use down to the Middle Ages and in some cases until as recently as the late 16th century. The Ordnance Survey map marks forts in Kilnamarve, Cloughlough, Aghawillan, Killahurk, Drumeela, Kilbracken, Corglass, Longfield, Gulladoo (2), Mullyaster (2), Drumshangore, Beaghmore, Beaghbeg, Drumergoole, Cornafest, Errew. The fort in Killahurk is a fine example of a two-ring fort. The circular ditch or fortification, which is all that survives of these forts, provided protection for the farmer, his animals and possessions from wild boars, wolves, eagles and marauders. Inside the ditch was a house, circular in shape and built of clay and wicker.

The fact that these ring forts survived the centuries was due to folk belief that they were the dwelling place of the fairies or 'good people' and therefore were in some way sacred and were not to be interfered with. Folklore everywhere abounds with stories of people coming into contact with these magical fort-dwellers. It was dangerous for a young girl to stray unattended near a fort after sunset lest she be enticed into the world of the fairies and a changeling left in her place who died shortly afterwards. The girl who was taken was seen afterwards riding on horseback with her companion near the fort. Other stories tell how she was snatched from the horse by a member of her family and brought back to the real world. There are numerous stories of people who played music at dances becoming involved in a music session with the fairies at a local fort.

It was considered unlucky until recently to interfere with a ring fort, to cut bushes growing on it, and people who were said to have died shortly afterwards or to have had bad luck. It is easy for us to discountenance these stories but our ancestors believed them and this helped to preserve the ruins of the homes of our early ancestors.

There are 2 crannóga in the parish, both in Kilnemar Lough. Like the ring forts these small artificial islands were also the homes of early farmers built out in lakes for purposes of protection. Access to them was by a causeway or by a boat or canoe cut out of a tree-trunk. They remained in use much longer than was originally thought. Some of them were still in use in nearby Cavan in Elizabethan times at the end of the 16th century. As no scientific survey has ever been made of Leitrim's crannóga it is sometimes difficult to say whether some of the small islands in our lakes are crannóga or just natural islands.

It is well to remember that the country in which these early settlers built their crannoga and ring forts was densely covered with primeval forest, undergrowth, lakes and swamp and would remain so for many centuries to come, Much of Leitrim's primeval forest was still intact in the 17th century and the last of it wasn't cut down until the middle of the 18th century.

In the first quarter of the 6th century a people known as the Conmaicne moved north from around the present Dunmore in County Galway and settled in Magh Rein (Fenagh). St Caillin of Fenagh was the patron saint of the Conmaicne. From here they peopled what is now South Leitrim, which became known as Magh Rein, and its inhabitants as the Conmaicne Magh Rein. They consisted of different family groupings-Muintir Eoluis, Muintir Cearbhallain, and Cinel Luachain. The most powerful of these was the Muintir Eoluis whose chiefs were drawn in later centuries from one or other branch of the Mac Rannall (Reynolds) family.

In Irish sources Muintir Eoluis, Conmaicne and Magh Rein are interchangeable names for the area we know as South Leitrim. At the end of the 8th century a second tribe know as the Ui Briúin moved north from mid-Roscommon and peopled Breifne or what is now North Leitrim, South Fermanagh and Cavan. Their chiefs from the 9th century onwards were the O'Rourkes.They exercised an overlordship over MacRanall and the Conmaicne and were sometimes refereed to in the Annals as King of Breifne and the Conmaicne. At some stage the Ui Briúin were able to annex permanently Cine Luachain (Oughteragh/Ballinamore), Droim-air-Bhealaigh (Drumreilly) and Magh Angaidh (Carrigallen) from the Conmaicne and incorporated them into Breifne. This explains why the three parishes, Ballinamore, Drumreilly Upper and Lower, and Carrigallen, were included in Kilmore, which was the diocese of the Ui Briúin and not, as would be expected, into the diocese of Conmaicne or Ardagh, seeing that they were originally part of the Conmaicne people, and that the boundaries of the new dioceses followed the boundaries of the Gaelic Kingdoms as far as possible.

Magh Angaidh is probably the oldest designation we have for all or part of the modern parish of Carrigallen although we do not know the precise extent of it. It lay to the south of Lough Finnmhaighe (the lake of the fair plain) or Garadice. John O'Donovan in his notes to his edition of the Annals of the Four Masters, says that by the early 1830's the area around Newtowngore was still known as the 'Moy'. Lough Finvoy or Finnmhaighe, occurs a number of times in the Annals. The Annals of the Four Masters has the following entry under the year: 'AM 2506; Age of the World 3506. Fifth year of Ermon an eruption of the following lakes: Loch Réin (Fenagh) Loch Finnmhaighe'.

Needless to say these early entries in the Annals are purely fictitious. Professor John P Duignan, in a lengthy article in the Proceedings of the Royal Irish Academy in 1922, entitled Crom Cruaich of Magh Slecht, in which he sought to establish the location of Magh Slecht quotes from the Tripartite Life of St Patrick as follows: Thereafter Patrick went over the water to Magh Slecht, a place in which the chief idol of Ireland, namely Cenn Cruiach, stood covered with gold and silver, and twelve other idols covered with bronze about him. When Patrick saw the idol from the water called Guth Ard etc. Duignan claims that the Guth Ard of the Tripartite Life survives in the name Garadice or Guth Ard Deas (Southern Guth Ard). To facilitate this theory he postulates the existence of a second stretch of water called Guth Ard Thuaidh or northern Guth Ard, consisting of the modern Ballmagauran, Derrycassan and Coologe lakes in Templeport parish. The name Garadice didn't come into common use until the 17th century.

By far the most important O'Rourke castle was not at Clooncorick near the present town of Carrigallen, but at Cloch Inse na dTorc (the stone fortress of Boar island) in Garadice, the remains of which are still to be seen on the present Cherry Island. Both the Annals of the Four Masters and the Annals of Connacht record under 1257 that Conn, son of Tiarnain O'Rourke, submitted to O'Connor and his son and ratified a treaty of peace with them and offered them their choice of the territory of Breifne. Cloch Inse na dTorc on Loch Finnmhaighe was also give to O'Connor who placed a garrison in it. Later in the year, O'Rourke attacked the fortress and captured it back and allowed the garrison to depart. In 1418, Eoghan, son of Tighearnan Mór O'Rourke, eligible prince of Breifne, was drowned in Loch Finnmhaighe on his way from Cloch Inse na dTorc to visit his father who was on his death bed. Under 1386, the Annals of Connacht record the death of Áine, daughter of Tadhg Mac Donnchada, wife of Tigherarnan O'Rourke, King of Breifne, at Tuaim Senchaidh or Toomonaghan (now Woodford demesne). From the 12th century down to the 15th century these two fortresses, one on the mainland and the other on the island, guarded the eastern frontier of west Breifne against attacks from the O'Reillys of east Breifne.

The Tripartite Life of St Patrick says that when Patrick was on his way to Magh Slecht to destroy Crom Cruaich, he founded a church and ordained a priest to look after it name Bruscus. The site of this Patrician church is thought to have been near Newtowngore. The ruin in the grounds of the present Church of Ireland in Newtowngore is more likely the medieval church of Moy, which was dedicated to St Patrick. Apart from this we know nothing of the early ecclesiastical history of Carrigallen. There are two holy wells dedicated to the saint, one in Aughawillan and the second in Beaghmore. Nearby the latter is a wart stone where people used to make the cure of the warts by washing them in the water which lay in a hollow in the stone.

The first reference we have in the Papal Annals to Carrigallen is in 1422 when Pope Martin V appointed Maurice O Flynn to the rectory of Cuylofflaynd of Inis Moyrmaghangody (Inis mor Magh Angaidh) in the diocese of Kilmore, which was vacant for so long a time 'that there was no certainty as to the true cause of its voidance'. Carrigallen doesn't seem to have been in use as the official title of the parish at the time. The name Cowlovlvoin also appears in an indenture made in 1585 between the Lord Deputy, Sir John Perrott and the principal native gentlemen of Breifne amongst them Felim Glas O'Rourke of Clooncorrick and Owen Mac Shane O'Rourke of Garadice. Elsewhere in the indenture the same Felim Glas is referred to as being from Cowlovlin. An inquisition taken at Dromahaire, July 22nd 1607, before Sir Anthony Sentleger to define the boundaries of the new county of Leitrim, says that Leitrim 'extendeth from Douffcoulofflyn mearynge upon Tayllagh Donoghy (Tullyhunco) to Bundoyne (Bundrowse near Bundoran). The indenture traces the boundary of the county westward, starting at 'the river Douffecowlofflyn', i.e. the river Duff of Cowlofflyn. The grants given under the plantation of Leitrim in 1621 are described as being in both the parish and the barony of Carrigallen.